1) Field of the Invention
This invention relates to the setting up of voice calls by communications devices in a digital network.
2) Prior Art
One way of setting up voice calls over an Integrated Services Digital Network (ISDN) by a computer involves an ISDN adapter installed in the computer which has a port for connection to a specially-adapted telephone or headset which is dedicated for use with the particular adapter.
This arrangement has a number of problems associated with it.
First, the telephone, being dedicated for attachment to the ISDN adapter, cannot be used standalone to communicate over the network. Secondly, when the computer is powered off, so is the telephone. This is a problem in emergency situations where power is lost and telephone contact is required. Thirdly, system and application software is required for the telephone to operate. Such system software normally needs homologation and, if not designed correctly, could lead to the application software also requiring homologation. Fourthly, if a software problem is encountered the user might have to restart the computer before the telephone can be used again. In the worst case, if the computer suffers a hardware failure then the telephone is not available until after the computer is repaired.